Well, LukeValantine pretty much summed up what the actual Chaos Warriors do already, so I'll do the same for Marauders.
Khorne: What spare time? If you're Khorne worshipper, then any moment you're not hacking someone's head off in the name of the Blood God is a moment wasted. Thus, a Khornate Marauder will be simply running around yelling and hacking people apart inside a red mist. They also gamble with Tzeentchians a lot, as this activity often leads to feelings of rage and subsequently violence.
Tzeentch: A Tzeentchian Marauder will be unravelling the secrets of the universe, and riddling his fellows to madness. They would also be practising some magic, and gambling due to the random chance involved. Sometimes, a Tzeentchian will delight in talking absolute gibberish to make their peers panic as they think their friend has succumbed to the greatest risk of worshipping Tzeentch.
Nurgle: A Nurglite Marauder would be looking after his weeping sores and buboes with the same care a mother gives a child. He could also be chasing around Slaaneshi Marauders, the Slaaneshis trying to avoid "Nurgle cooties."
Slaanesh: This is spare time? A Slaanesh Marauder's spare time is eternal! They just do all they can to get some twisted pleasure. We're talking drugs and torture here. They also write plays, novels and poems, and compose symphonies whilst painting the greatest artworks you can see in the Warhammer world, including the famed Moaning Lisa. Anything else is behind a curtain, and you can hear sounds of passion and thumping as it's going on. For the slowest among you, they'd be having sex. Oh, and don't forget the running away from "Nurgle cooties"!
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I have spent the last 25 minutes doing reconnaissance on my kitchen for operation: Cup of tea.